Sonic agitation of molten metal

ABSTRACT

Simultaneous fluxless joining, tinning and/or coating of components or workpieces is effected by the use of a sonically agitated molten metal bath maintained at a uniform temperature and contained in a vessel comprised of a curved (in cross section), solid, unitary shell. The sonic agitation is provided by multiple arrays of sonic energy transducers disposed about and along the shell, and in energy transfer relationship with the bath via the shell. The arrays of transducers are grouped, and the groups individually energized by sonic power generators each having means for controlling the sonic power output thereof, as well as the sonic frequency, to provide individually controllable zones of sonic energy within the vessel and molten metal bath.

' [22] Filed:

United States Patent [191 Brouwer et al.

2 SONIC AGlTATION OF MOLTEN METAL [75] Inventors: Nicholaas L. Brouwer,Allegheny Township, Westmoreland County;

David E. Smucker, New Kensington, both of Pa.

[73] Assignee: Aluminum Company of America, Pittsburgh, Pa.

Sept. 20, 1973 [21] Appl. No.: 398,946

8/1973 Watson 228/36 [111 3,822,820 451 July 9,1974

Primary ExaminerGerald A. Dost Attorney, Agent, or Firm-Elroy Stickland[5 7] ABSTRACT Simultaneous fluxless joining, tinning and/or coating ofcomponents or workpieces is effected by the use of a sonically agitatedmolten metal bath maintained at a uniform temperature and contained in avessel comprised of a curved (in cross section), solid, unitary shell.The sonic agitation is provided by multiple arrays of sonic energytransducers disposed about and along the shell, and in energy transferrelationship with the bath via the shell. The arrays of transducers aregrouped, and the groups individually energized by sonic power generatorseach having means for controlling the sonic power output thereof, aswell as the sonic frequency, to provide individually controllable zonesof sonic energy within the vessel and molten 1 metal bath.

11 Claims, 2 Drawing Figures 1 SONIC AGITATION OF MOLTEN METALBACKGROUND OF THE INVENTION The present invention relates generally tothe sonic agitation and resulting cavitation in a molten metal bath, andparticularly to an arrangement whereby, in a solder bath medium,maintained at a uniform temperature, cavitation is produced to providereliable, consist ant joining, tinning and/or coating of components without the need of flux, and of the type required for industrial,production purposes. The term sonic energy as used herein, refers tosubsonic, sonic or ultrasonic frequency energies.

The use of sonic energy sources to agitate molten metal baths are wellknown. However, past and present apparatus employing such sources havecertain disadvantages for ambient and elevated temperature applicationsin an industrial environment. The majority of vessels employed in theindustry for containing sonically agitated moltenmetal have a generallyrectangular or square configuration in cross section, the vessel beingeither cast in such a configuration or fabricated from metal plateswelded togetheralong abutting edges to form a square or rectangularlyshaped vessel. Such a vessel configuration provides a bottom shellsurface of limited area for attaching sonic transducers, therebylimiting the number of transducers that can be used, and thus limitingthe sonic power transmitted into the molten metal. Generally, the sidewalls of a square or rectangular shaped vessel do not readily lendthemselves for the attachment of a large number of sonic energytransducers because the sidewalls are usually employed to apply heat tothe vessel and thus to the molten metal contained therein. 1

Further, rectangularly shaped vessels tend to be highly rigid such thatthe mechanical forces produced in the shell of the vessel by the sonicagitation, and resulting cavitation of the molten metal, fatigue theshell, particularly along the right angle intersections of the side andbase walls thereof, the intersections forming areas of stressconcentration.

If the vessel is fabricated by welding square or rectangular platestogether, the welds are located along the intersections of the sides andbase and thus at the areas of stress concentration such that welds areweakened by the sonic agitation and cavitation. Those welds that extendlengthwise of the vessel are especially susceptible to the detrimentaleffects of the mechanical forces generated within the vessel shell sincethe magnitude of the'sonic energy is substantially greater in the morecentral areas of the base of the vessel.

In addition, welded areas of a vessel may be subject to corrosive attackby components of the molten medium, such as the zinc in a zinc solderbath. As a result of such fatigue and attack, the welds and vessel wallsare weakened such that over a period of time the vessel must either berepaired or replaced.

A problem associated with past and present sonic energy solderingtechniques employing a bath of molten metal solder is the unevenness ornon-uniformity of the agitation and cavitation along the base of thevessel, where the transducers are attached, such that sonicallyquiescent or dead zones occur within the medium of the bath along withzones having a high concentration of sonic energy. Such zones becomeparticularly critical when a plurality of components having amultiplicity of joining surfaces, occupying a broad area within thevessel, are immersed in the bath to effect simultaneous soldering of thejoining surfaces. An example of a structure having such multiplicity ofjoining surfaces is a heat exchanger having a multiplicity of socketjoints formed by U-shaped, return bend tubes disposed on the ends ofelongated tubes of the heat exchanger to serially connect the tubestogether. In the dead or less active zones of the solder bath, little orno soldering or joining takes place so that any of the multiple joiningsurfaces located in such zones are either not soldered at all or areinadequately soldered and joined. Such a soldering arrangement is thusunsuitable for soldering heat exchangers since all joints in a heatexchanger must be equally and satisfactorily soldered or the heatexchanger is or soon becomes a defective unit with normal use thereof.

BRIEF SUMMARY OF THE INVENTION Briefly, the present invention overcomesthe problems and disadvantages of prior and present apparatus employedto sonically agitate molten metal baths by the use of a vessel comprisedof a unitary, solid, curved shell in cross section, the unitary shellproviding a vessel having no welds extending between the ends of thevessel, and no welds at all if the vessel is made as a one piece unit,such as would be provided by a castingor forging process, for example.In this manner, there are no welds to be severely attacked'by acomponent or components of the molten metal bath andby the cavitationproduced in the bath medium.

Maximum uniformity of sonic agitation and resulting cavitation of themolten metal within a prescribed work area inlthe vessel is effected byuse. of circumferential arrays of sonic energy transducers locatedaround the curve of the vessel shell and disposed in sonic energytransfer relationship with curved, outer surface of the shell.

Preferably, the arrays of sonic energy transducers are attachedrespectively to corresponding arrays of sonic energy coupling devicesprojecting outwardly from the curved, outer surface of the vessel shell.

The arrays of sonic transducers and coupling devices are divided intogroups and energized by a correspond-' ing plurality of generators toprovide individual control and/or tuning of the groups of transducersand thus provide sonic power input control to the areas of said I vesselassociated respectively with the corresponding transducer groups.

Between the coupling devices and disposed closely adjacent the vesselshell are located heaters that heat and maintain the molten metal bathat a uniform, elevated temperature, i.e., for example, on the order of760F, the transducers being preferably located away from the heaters bythe extent of coupling devices.

THE DRAWING face of the shell in accordance with the principles of I theinvention; and

FIG. 2 is a side elevation view of the structure of FIG. 1, with thevessel proper being shown in section.

PREFERRED EMBODIMENT OF THE INVENTION Referring now to FIG. 1 of thedrawing, a soldering vessel or tank is shown in cross section, thevessel being comprised of a unitary, solid and curved wall or shell 12,the curve of the shell preferably extending the full length thereof, asindicated in FIG. 2. As shown in the figures, the shell may haveopposed, outwardly extending flange portions 13 that extend the lengththereof.

The vessel 10, being primarily a single piece unit has no weld areasextending the length thereof for attack by components of the moltenmetal (not shown) contained therein or by the cavitation of the bath, asdiscussed earlier. The vessel includes end wall portions 14 and 16, asshown in FIG. 2, which may be an integral, unwelded portion of the shell12, or, the end walls 14 and 16 can be made separately from shell 12 andjoined to the ends of the shell by weld seams (not shown) located at theintersections of the curved ends of the shell and the planar surfaces ofthe end walls. Such end welds and seams, however, are not subject tosevere sonic agitation and resulting cavitation of the bath since theintensity of sonic energy adjacent the ends of the vessel is minimal incomparison to that existing along the more central areas of the vessel.

On and around the outside surfaces of the curved shell 12 are mounted,as shown in FIG. 1, four, spaced apart elongated sound energy couplingbars 18, (only one such bar being visible in FIG. 2), the number (four)of coupling bars depicted in FIG. 1 being given only for purposes ofillustration. As explained hereinafter, the number of coupling bars,coupling extensions and sonic energy transducers are chosen on the basisof such factors as the amount of sonic power desired or required for aparticular vessel and operation.

The coupling bars 18 may be formed as an integral part of the shell 12,thereby providing a continuous path between the bars and shell formaximum transfer of sonic energy into the vessel from the bars.

As shown in FIG. 2, the coupling bars have outwardly projecting soundenergy coupling extensions, such as horns or studs 20 spaced along thelength of the bars, that provide multiple arrays of the coupling devicesextending lengthwise of the vessel. In FIG. 1, only one such array isvisible.

If the coupling bars 18 are not formed as an integral part of shell 12,the bars should be attached to the shell in a manner that presents aminimum acoustical impedance to the sonic energy to be directed into thevessel. This can be accomplished with means and materials that produce agood metallurgical and sonic bond between each bar and the shell, forexample, as provided by the full penetration welds 22 shown in FIG. 1,which welds extend the length of the bars. Full penetration welds andgood metallurgical bonds of similar materials provide minimum acousticalimpedance to the sound energy generated by sonic energy transducers 24attached to the coupling extensions 20, and presently to be described,to obtain maximum transfer of the sound energy from the transducersurfaces, coupling extensions and bars to the shell 12, and thus intothebath contained in the vessel 10.

With the coupling bars 18 extending along the length dimension of thevessel, the bars serve further to strengthen the vessel, and touniformly distribute sonic energy over the vessel area.

Sonic energy transducers 24 are shown attached to the ends of thecoupling extensions 20 remote from the shell 12, the transducers beingpreferably magnetostrictive devices schematically represented in thefigures by cores 26 and windings 28, the transducers, like the couplingextensions, being circumferentially spaced apart around the curve of theshell, and along the length thereof (FIG. 2) to provide multiple arraysof sonic sources. The transducers 24 are preferably magnetostrictivebecause such transducers have metallic cores that can be brazed orwelded to a metal surface in a manner that presents a minimum impedanceto the sonic energy developed in the core by its winding whilesimultaneously providing a high strength joint particularly suitable forindustrial purposes. For example, if the coupling extensions arestainless steel and the cores of the transducers are comprised of nickelor nickel alloy laminations, the laminations can be joined to the endsof the coupling extensions by silver soldering or brazing the joiningmaterials providing a high strength, good metallurgical bond between thelaminations of the transducers and the stainless steel of the couplingextensions, and thus a minimum acoustical impedance at the interfacesbetween the transducer cores and the coupling extensions. Further,magnetostn'ctive transducers are reliable, rugged devices that canwithstand the high temperatures associated with molten metal.

In addition, to further insure maximum transfer of acoustical energyinto the molten metal within the vessel 10 the thickness dimension ofthe shell 12 and the length of each coupling extension 20 (including thebar portion 18) together is preferably one half wave length long at theresonant frequency of transducers 24.

As indicated only schematically in FIG. 1 of the drawing, between theperipherally spaced locations of the coupling bars and transducers, andextending lengthwise of the vessel 10 are located heating devices 29 forheating and maintaining the molten metal bath within the vessel 10 at anelevated, molten temperature. Heating devices suitable for such apurpose are preferably elongated, electric resistance heating rodslocated in close proximity to the vessel shell 12 but with minimumphysical contact therewith to minimize damage of the rod elements by thesonic vibration. In combination with such rods, it is preferable to usereflectors located behind the rods and facing in the direction of thevessel shell, the reflectors with the rods, serving to direct radiantheat, i.e., the heat radiated by the rods, at the vessel shell, when therod elements conduct appropriate amounts of electrical current.

Such heating devices are particularly advantageous in heating anindustrial soldering vessel since they can be conveniently disposed toevenly heat the vessel and soldering bath, and can be precisely,automatically controlled by thermocouples, and associate electricalapparatus, operatively associated with the vessel or with the soldercontent within the vessel.

The desirability of such control is especially critical when cavitationof the soldering bath is employed in the soldering process. Thecavitation phenomenon can be aggressive to the point of attacking anddestroying the metal of components immersed in the bath. The velocity ofsound energy in the bath, which energy produces the cavitation, isitself a function of the temperature of the bath. Thus, by evenly andprecisely controlling the temperature of the bath through the vessel,control of the velocity of the sound, and thus cavitation, in the bathcan be effected throughout the bath medium. In this manner, only theoxides and other impurities on the components to be soldered are removedtherefrom by the cavitation, and since the cavitation is relativelyuniform throughout the bath, the soldering is even and effectiveregardless of the location of the components within the bath.

There are substantial variations in the sizes and configurations ofvessels designed to hold molten metal for sonic agitation, and in theworkpieces and components disposed in the molten metal for coating thejoining purposes. If, for example, the components to be soldered in asoldering bath occupy only a limited area within a large vesselcontaining the bath, it is desirable, if for no other purpose than thesaving of electrical power, to activate with sonic energy substantiallyonly the area of the bath occupied by the components.

In addition, vessels having different sizes and shapes have differencesonic resonant frequency characteristics, and these characteristicschange to an extent when a workpiece or pieces are disposed in themolten metal bath, the degree of change depending, in turn, upon thesize and configuration of the workpiece. Thus, in a vessel containing amolten metal medium designed to operate efficiently at the resonantfrequency of a particular sonic energy transducer, the load on thetransducer is changed somewhat when the workpiece or pieces are insertedin the vessel and molten metal thereby changing somewhat the resonantfrequency of the transducer. Thus, to effect optimum, maximum sonicenergy transfer in a vessel containing a molten metal medium havingworkpieces disposed thereof of a particular number and configuration, itis desirable to be able to tunethe vessel or portions thereof byapplying thereto a sonic frequency that is the resonant frequency of thetransducer as it is affected by the load, i.e., by the configuration ofthe workpiece and the alteration of the vessel configuration when theworkpiece is disposed in the vessel. The tuning accomplished hereeffects optimum conversion of the electrical energy, produced bygenerators presently to be described, to mechanical, sonic energy at theresonant frequency of the total vessel and molten metal structure.

With these considerations in mind, the present invention includesgrouping the transducers and coupling extensions to provide selectivecontrol of sonic power into the vessel, and selective tuning of thevessel, as shown and suggested schematically in FIG. 2. Moreparticularly, the twelve transducers 24 associated with each couplingbar 18 are shown electrically divided into three groups of fourtransducers by being respectively electrically connected to threeelectrical power generators 32, 33 and 34 designed to energize the threegroups at their resonant frequency. Thus, with the arrangement depictedin the drawing, in which four coupling bars 18 each having twelvecoupling extensions 20 and transducers 24, twelve generators arerequired, though only three are shown in FIG. 2. This grouping, however,as well as the number of transducers and coupling devices, is given byway of example only, the number of generators, transducers and groups oftransducers being chosen on the basis of such factors as the size of thevessel tobe employed and the power requirements for a particular volumeand type of molten metal to be agitated.

As depicted in FIG. 2 by variable resistances 36, each of the generatorshas means to control the level of its power output to its particulargroup of four transducers, thereby providing means to control both themagnitude and the locations of sonic energy input to the molten metalwithin vessel 10.

All of the generators can be triggered synchronously by a single,common, variable oscillator 38 (FIG. 2), designed to oscillateapproximately at some range around the resonant frequency of thetransducers 24, or, each generator can be individually triggered andtuned by its own variable oscillator, such oscillators being shown indash outline in FIG. 2, and indicated by numerals 42, 43 and 44. With avariable frequency oscillator associated with each generator, theelectrical output of each generator, and thus the sonic frequencyproduced by its associated array of transducers, can be tuned to theresonant frequency of the transducers as they are loaded and affected bythe geometry of the vessel 10 with workpieces disposed therein. In thismanner, maximum transfer of sonic power to the molten metal, and to thearea thereof associated with the particular group of transducers beingtuned, is obtained.

The term solid as used herein in reference to the vessel refers to ashell structure that has no or substan tially no perforations oropenings.

While the invention has been described in terms of preferredembodiments, the claims appended hereto are intended to encompass allembodiments which fall within the spirit of the invention.

Having thus described our invention and certain embodiments thereof, weclaim:

1. In combination, a vessel for containing molten metal at elevatedtemperatures, the vessel comprising a unitary, solid, curved shell incross section, multiple arrays of sonic energy transducers spaced apartabout and along the outside of said shell, and in sonic energy transferrelationship with the shell for directing sonic energy through the shelland into a work area of the vessel whenthe transducers are energized, aplurality of electrical power generators having means for individuallycontrolling the power output thereof, and an oscillator for commonly,synchronously triggering said generators, groups of the arrays oftransducers being respectively electrically connected to and energizedby said generators for providing individually controllable zones ofsonic energy within the vessel, and means for uniformly heating thevessel and molten metal.

2. The combination of claim I in which the arrays of sonic'energytransducers are attached respectively to corresponding arrays of sonicenergy coupling devices disposed about and along the outside of thecurved shell and in sonic energy transfer relationship with the shell.

3. The combination of claim 2 in which the coupling devices are attachedto the vessel shell by full penetration welds.

4. The combination of claim 2 in which the coupling devices are formedas an integral part of the vessel shell.

5. The combination of claim 2 in which the coupling devices includeelongated, sound energy coupling bars extending lengthwise of thevessel.

6. The combination of claim 2 in which the coupling devices includearrays of outwardly projecting, sonic energy coupling extensionsdisposed in sonic energy transfer relationship with the vessel shell.

7. The combination of claim 6 in which the coupling devices includeelongated, sound energy coupling bars extending lengthwise of thevessel, and the coupling extensions form an integral part of theelongated coupling bars.

8. The combination of claim 1 in which the heating means comprise aplurality of heaters disposed around the outside surface of the vesselshell.

9. ln combination, a vessel for containing molten metal at elevatedtemperatures, the vessel comprising a unitary, solid, curved shell incross section, multiple arrays of sonic energy coupling devices spacedapart about the outside of said shell, with one end of each devicedisposed in sonic energy transfer relationship with the shell fordirecting sonic energy through the shell, multiple arrays of sonicenergy transducers respectively attached to the ends of said couplingdevices remote from the shell, the arrays of devices and transducersbeing capable of directing the major portion of the sonic energyproduced by the transducers, when the transducers are energized, into awork area of the vessel, a plurality of electrical power generators eachhaving an oscillator that individually triggers and tunes the generatorat the frequency of said oscillator, groups of the arrays of thetransducers being respectively electrically connected to and energizedby the generators to provide individual tuning of zones of sonic energywithin the vessel for optimum transfer of sonic energy within saidzones, and means for uniformly heating the vessel and molten metal.

10. The combination of claim 9 in which the vessel includes two wallportions closing the respective ends of the shell, and joined to theends of the shell.

11. In combination, a vessel for containing molten metal at elevatedtemperatures, the vessel comprising a solid, curved shell in crosssection and wall portions closing the respective ends of said shell,said wall portions being welded to the ends of said shell, multiplearrays of sonic energy coupling devices spaced about the outside of theshell, with one end of each device disposed in sonic energy transferrelationship with the shell, multiple arrays of sonic energy transducersrespectively attached to the ends of the coupling devices remote fromthe shell, the arrays of devices and transducers being capable ofdirecting the major portion of the sonic energy produced by thetransducers, when the transducers are energized, into a work area of thevessel, a plurality of electrical power generators having means forindividually controlling the power output thereof and an oscillator forcommonly, synchronously triggering said generators, groups of saidarrays of transducers being respectively electrically connected to andenergized by said generators for providing individually controllablezones of sonic energy within the vessel, and means for uniformly heatingthe vessel and molten metal.

1. In combination, a vessel for containing molten metal at elevatedtemperatures, the vessel comprising a unitary, solid, curved shell incross section, multiple arrays of sonic energy transducers spaced apartabout and along the outside of said shell, and in sonic energy transferrelationship with the shell for directing sonic energy through the shelland into a work area of the vessel when the transducers are energized, aplurality of electrical power generators having means for individuallycontrolling the power output thereof, and an oscillator for commonly,synchronously triggering said generators, groups of the arrays oftransducers being respectively electrically connected to and energizedby said generators for providing individually controllable zones ofsonic energy within the vessel, and means for uniformly heating thevessel and molten metal.
 2. The combination of claim 1 in which thearrays of sonic energy transducers are attached respectively tocorresponding arrays of sonic energy coupling devices disposed about andalong the outside of the curved shell and in sonic energy transferrelationship with the shell.
 3. The combination of claim 2 in which thecoupling devices are attached to the vessel shell by full penetrationwelds.
 4. The combination of claim 2 in which the coupling devices areformed as an integral part of the vessel shell.
 5. The combination ofclaim 2 in which the coupling devices include elongated, sound energycoupling bars extending lengthwise of the vessel.
 6. The combination ofclaim 2 in which the coupling devices include arrays of outwardlyprojecting, sonic energy coupling extensions disposed in sonic energytransfer relationship with the vessel shell.
 7. The combination of claim6 in which the coupling devices include elongated, sound energy couplingbars extending lengthwise of the vessel, and the coupling extensionsform an integral part of the elongated coupling bars.
 8. The combinationof claim 1 in which the heating means comprise a plurality of heatersdisposed around the outside surface of the vessel shell.
 9. Incombination, a vessel for containing molten metal at elevatedtemperatures, the vessel comprising a unitary, solid, curved shell incross section, multiple arrays of sonic energy coupling devices spacedapart about the outside of said shell, with one end of each devicedisposed in sonic energy transfer relationship with the shell fordirecting sonic energy through the shell, multiple arrays of sonicenergy transducers respectively attached to the ends of said couplingdevices remote from the shell, the arrays of devices and transducersbeing capable of directing the major portion of the sonic energyproduced by the transducers, when the transducers are energized, into awork area of the vessel, a plurality of electrical power generators eachhaving an oscillator that individually triggers and tunes the generatorat the frequency of said oscillator, groups of the arrays of thetransducers being respectively electrically connected to and energizedby the generators to provide individual tuning of zones of sonic energywithin the vessel for optimum transfer of sonic energy within saidzones, and means for uniformly heating the vessel and molten metal. 10.The combination of claim 9 in which the vessel includes two wallportions closing the respective ends of the shell, and joined to theends of the shell.
 11. In combination, a vessel for containing moltenmetal at elevated temperatures, the vessel comprising a solid, curvedshell in cross section and wall portions closing the respective ends ofsaid shell, said wall portions being welded to the ends of said shell,multiple arrays of sonic energy coupling devices spaced about theoutside of the shell, with one end of each device disposed in sonicenergy transfer relationship with the shell, multiple arrays of sonicenergy transducers respectively attached to the ends of the couplingdevices remote from the shell, the arrays of devices and transducersbeing capable of directing the major portion of the sonic energyproduced by the transducers, when the transducers are energized, into awork area of the vessel, a plurality of electrical power generatorshaving means for individually controlling the power output thereof andan oscillator for commonly, synchronously triggering said generators,groups of said arrays of transducers being respectively electricallyconnected to and energized by said generators for providing individuallycontrollable zones of sonic energy within the vessel, and means foruniformly heating the vessel and molten metal.